Objectives: To investigate the controversially discussed relationship between tumor size and the occurrence of primary synchronous metastatic disease in renal cell cancer (RCC). Patients and Methods: A consecutive RCC cohort of 2,058 patients (150 primary metastatic) who underwent surgery between 1995 and 2010 was investigated. Rates of synchronous metastases were calculated for stratified groups of tumor size. Uni- and multivariate logistic regression models were calculated for the correlation of tumor size with primary metastatic disease. Results: The rate of metastatic disease increased with increasing tumor size. Tumor size was significantly correlated with synchronous metastatic disease (p < 0.001, c-index 0.772), but for RCCs ≤4 cm in size no significant correlation was found. Regarding tumors ≤5 cm in size, the correlation became significant (p = 0.028, c-index 0.621). A multivariate logistic regression model for the prediction of synchronous metastatic disease including tumor size, age and comorbidity yielded a significant c-index of 0.82 and was used to construct a nomogram. Conclusion: Our data confirm the correlation between tumor size and the rate of synchronous metastatic disease. Small renal tumors <4 cm in size have a low risk of synchronous metastatic disease. The risk becomes significantly associated with tumor size for tumors ≤5 cm.

The postoperative Karakiewicz nomogram provides a good concordance in this external cohort and is reasonably calibrated. It may overestimate tumor-specific survival in high-risk patients, which should be kept in mind when counseling patients. A positive net benefit of nomogram predictions was proven.

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